In the aircraft industry there are a myriad of situations where hydraulic power is called upon in airplanes to effect the actuation of a component. The component actuated may be a flap or other flight control surface. The never ending quest for weight reduction and system efficiency has been heightened by the upward spiraling increased cost of fuel, as well as the more exotic environments experienced by high performance fighter aircraft.
Amongst the more recent advances in hydraulic powered actuation systems that embraced the desirable proposition of weight reduction and improved efficiency, is that invention shown and described in the Flippo, U.S. Pat. No. 4,191,094. The Flippo patent shares the same assignee as the applicants in the subject application.
The Flippo patent is directed to a power drive unit for the operation of an aircraft thrust reverser structure in an aircraft engine. The thrust reverser structure is operable between a stow and deploy positions and includes a bi-direction hydraulic motor having a variably positionable wobbler for controlling displacement of the motor. A control structure is provided for causing fluid flow through the motor in either of two directions. The control structure further includes a piston connected to the wobbler for setting the motor at either minimum or maximum conditions or any condition therebetween. A servo valve is also provided for setting the position of the piston in the control cylinder and a differential area piston is operatively connected to the servo valve for positioning thereof. The piston is responsive to the pressure drop across the motor in either direction of operation thereof to set the motor displacement at the least value possible for the load condition on the motor. Flippo also requires reversing hydraulic pressure to the input ports of the hydraulic motor to reverse the direction of the motor, and Flippo controls the speed of his motor by means of a dissipative discharge valve.
The invention to be described hereinafter advantageously distinguishes over Flippo in that the hydraulic motor displacement is additionally controlled as a function of the velocity and position of the power drive output while simultaneously providing regenerative hydraulic power to the control system whenever there is an aiding load experienced by the power drive unit output. The invention to be described hereinafter additionally distinguishes over Flippo in that hydraulic motor reversal does not require the reversing of hydraulic pressure to the ports of the motor and does not require an energy dissipative discharge valve to control the speed of the hydraulic motor.
The advanced state of the art is also shown and described in the U.S. Pat. No. 4,210,066 to Aldrich, which is directed to a power drive unit and includes a bi-directional hydraulic motor having a variably positionable wobbler for controlling displacement of the motor. A control structure is provided that includes a valve for causing fluid flow through the motor in either of two directions. A control cylinder and piston are connected to the wobbler for setting the motor at either minimum or maximum displacement conditions. The Aldrich patent shares the same assignee as the applicants in the subject application.
The Aldrich power drive unit, as advanced as it is, still does not provide the advantageous features enumerated in detail in respect of Flippo above.
The U.S. Pat. No. 3,302,389 to Cadiou, is directed to a regulating device for a barrel-type hydraulic transmission and represents a prior art teaching of a wobbler controlled hydraulic motor wherein the wobbler position and hence motor displacement is a function of input engine velocity, input command and wobbler position. No suggestion is made in Cadiou that the output velocity and position of the drive unit shown functions to control the position of the wobbler as will be evidenced in the description of the invention that will follow.